Nicotiana tabacum Callus Studies III. Size and Shape of Vascular Elements

Abstract

Summary Tracheary and sieve elements induced in vitro in Nicotiana pith callus are as wide as but about five times shorter than those in the internodes of the plants from which the expiants derive. Shape, especially in the tracheary elements, is extremely irregular. Giant tracheidal cells differentiate in the presence of indoleacetic acid and gibberellin in explants which otherwise have undergone limited amounts of callus development. These tracheids are more regular in shape and are considered to be the direct redifferentiation products of the pith parenchyma cells. Although the sieve elements show much less variation in shape than do the tracheary elements, the slopes of their end walls are more varied than those of sieve elements in the intact plant.